Betula occidentalis is a common, streamside, shrubby birch throughout much of the Rocky Mountains, extending eastward to northwestern Ontario. It has been widely known by the later name B . fontinalis because of questions concerning the legitimacy of Hooker's epithet (J. R. Dugle 1966). Recent changes to the International Code of Botanical Nomenclature (W. Greuter et al. 1994) have clarified the situation, however, and the consensus now is that the earlier name is correct. E. Hultén (1968) believed that the species in Alaska that has been called B . occidentalis consists of an extensive hybrid swarm between B . neoalaskana (as B . resinifera ) and B . glandulosa . The studies of J. R. Dugle (1966) do not support a hybrid origin of B . occidentalis in other parts of its range. Additional study will be needed to resolve this problem, both in Alaska and southward.